CIVL473 Fundamentals of Steel Design

Prepared By

Assoc.Prof.Dr. Murude Celikag

CHAPTER 7

Connections

7.

7. Connection Design

Why do we need connections?Connections are essential to join discontinuous

elements, e.g. beams and columns, to create

structures.

a) Welded Connections• Fillet Welds: Weld metal is outside the

profile of connected element• Butt Welds: Weld metal is deposited within

the profile of the connected elements

DOUBLE LEFT WELD (any type of loading)

SINGLE LEFT WELD (shear only)

LAP SPLICE(any type of loading)

DOUBLE V BUTT WELD SINGLE V BUTT WELD

SINGLE BEVEL BUTT WELD

Fig. 7.1 Fillet Welds

Fig. 7.2 Butt Welds

b) Bolted Connections: Generally used for site connections

• Bearing (ordinary) Bolts in Clearance HolesAdvantages – low cost for buying and installingDisadvantages – slips into bearing at a low load shear

• High Strength Friction Grip Bolts (HSFG)Advantages – high stiffness in shearDisadvantages – expensive

• Other Components of ConnectionsFlats, plates, angles, tees, gusset plates, etc.

Fig. 7.3 Bearing (ordinary) BoltsFig. 7.4 Examples of other components in connections

Why connection design is important?Strong connections are essential to transfer the loads

among structural members. Weak connections could

cause failure of any structure.

a) Economy of StructureDesigners of connections should bear in mind the

following regarding economical fabrication and erection

process.

Maintaining ease of access for welding

Optimizing the use of automatic equipment

Minimizing precise fitting

Achieving repetition of standard details, etc.

Ease of access for site bolting

Provision for supporting the element self-weight

quickly so that the crane can be released

Ease of adjustment for alignment

Simplicity and repetition, etc.

b) Economy of DesignConnection design is a significant part of the total

design cost for the structure. Most connection design

should be a simple, routine matter. A simple calculation

to determine the minimum number of bolts (based on

shear and bearing capacity) would be sufficient.

Design approach for connections?Connection behaviour is both complex and more

variable than the connected elements.

Geometric imperfections due to welding distortion,

cutting and machining imperfections, and permitted

misalignment of clearance holes for bolts between

plies

Residual stresses and strains due to lack of fit and

welding shrinkage

Geometric complexity within the connection

Fig. 7.5 Simple web cleat beam-column connections: contrast between design assumptions and detailed behaviour

Fig. 7.6 Bolt force distribution in beam-column connections with end-plates

Local elements in connectionsUltimate strength design methods are appropriate for

the design of bolts and welds. Deformation may be

limited at times to prevent corrosion. The following are

the effects relevant to connection design.

a) Web yielding at points of concentrated load orreactionConcentrated load at bearings and intermediate points

on girder flanges may produce compressive yielding in

the adjacent web. The extent of the concentration

depends on the effective stiff length of the bearing

surface and the depth of material between the seating

and the girder web (Fig. 7.9).

7.7 7.8

b) Web buckling at points of concentrated load or reaction

c) Local bending of plates or flanges d) Eccentric connection to tie memberse) Shear in panels at member junctions

Fig. 7.9 Web crushing or bearing

Fig. 7.10 Length of bearing

Fig. 7.11 Effective bearing zone in beam web

7.12

7.13

Fig. 7.14 Beam-to-beam connections: erection-stiff

Fig. 7.15 Beam-to-beam connections: fully rigid